It is known that the industry involving the production of sheet metal items uses panelling machines that allow a series of bends to be made on the same piece of sheet metal, in a controlled and totally automatic way, so as to obtain a finished product such as, for example, a cooker extractor hood or a shelf.
It is also known that panelling machines or sheet metal bending machines normally consist of:                a fixed bed for supporting the material, for example sheet metal, to be pressed;        a support frame for a clamping press;        a punch or presser, forming part of the press, and a corresponding counter-press or counter-blade, acting as clamping means for the material during bending;        one or more auxiliary elements, for manual or automatic insertion, commonly called auxiliary tools, forming part of the press, to be positioned between the punch and the corresponding counter-punch or counter-blade, specifically constructed and acting as clamping means for the material during bending of particular pieces;        one or more bending blades which can be moved towards the material being processed;        appropriate kinematic systems designed to move the blade or blades along the bed for the shaping of the piece clamped between the punch and the counter-punch;        appropriate kinematic systems designed to move the punches which allow the clamping and release of the sheet metal, also in the presence of auxiliary tools, guaranteeing a pressing force that always corresponds to the length and thickness to be bent;        means of movement for the sheet metal, or the section, in order to move it near the blades in working conditions;        transducers and sensors of various types, to control the process, connected to an electronic control unit governing the production process.        
A bending machine of the known type described above, marketed by the applicant, comprises a blade-holder structure with a “C”-shaped cross-section, mobile in two directions at right angles to each other with respect to a fixed bed, on which the bending blade(s) is(are) fixed.
The profile of the bend that can be obtained on a known automatic panelling machine is not just the classic 90° profile that can be obtained with a manual bending machine. The simultaneous control of the positioning of the blade and of the pressure exerted on it make it possible to obtain radial profiles.
The use of traditional blades, particular tools and dies during the bending cycle also makes it possible to obtain special profiles, without it being necessary for the operator to intervene to vary the length or the special tool used.
Traditionally constructed blades are supported by a C-shaped structure mounted on the main frame and the unit comprises two blades: the upper one for shaping negative bends (facing downwards) and the lower one for positive bends (facing upwards).
The system controls the size of the angles and the thickness of the sheet metal, adjusting the position of the blades by means of proportional valves. All the movements are carried out by proportional-control hydraulic cylinders. A special mechanism guarantees the parallelism of the bending unit movements.
The punch or upper presser element is modular in order to obtain the appropriate size of the piece to be machines and contractable to allow extraction of the machined piece. It is mounted on an electrowelded structure with four arms and hinged to the rear part of the main frame.
Thanks to the action of appropriate mechanisms each segment can be released and repositioned very easily, since a trigger prevents the segment falling from the tool-holder bar.
The movements of the C-shaped structure and of the upper tool are controlled by hydraulic cylinders rather than by electric motors.
The position of the cylinders, or electric motors, is controlled by a special system (numerical control or similar) in such a way as to allow the greatest degree of precision during all the bending stages.
Traditional hydraulic panelling machines, like other panelling machines on the market, are equipped with a kinematic system which determines and controls the movement of the blade-holder unit.
This structure can in some cases be the pentalateral type, that is to say consisting of a closed kinematic chain with five members connected by five kinematic pairs.
In hydraulic machines the traditional pentalateral type kinematic chain is used, however, to give the machine torsional rigidity and does not therefore have specific mechanical functions.
In the patent application PCT/IT2004/000581 the same applicant invented a particular kinematic chain with two degrees of freedom, currently the only one that allows electrical control of the bending blade.
The same applicant recently introduced a series of panelling machines on the market which are characterised by electrical control of the bending axes and of the punch/presser, that is to say all the axes that provide torque and absorb significant power exploiting the invention described above.
This new series of machines, well received by the market, presents the following features:                reduced energy consumption (more than halved compared to a corresponding hydraulic machine);        less noisy and more respect for the environment;        better control of the pressing and bending axes with consequent better results in terms of component finish;        improved performance in terms of speed and cycle time compared with all the machines currently on the market;        
The kinematic designs for control of the punch/presser in machines currently produced are shown in FIGS. 1a to 3a, while FIGS. 1 to 3 show the respective machines, characterised by the use of a mechanical design defined articulated quadrilateral.
As can be seen in the figures this is the kinematic design defined as four bar linkage which works close to a singular configuration in order to ensure an adequate pressing force for kinematic amplification of the delivered torque.
FIGS. 1 to 3 show the components of the punching machines currently produced with a four bar linkage structure. In the three figures, which represent the known art, A indicates the frame, B the driving crank, C the connecting rod, D the presser arm and E an auxiliary tool. FIGS. 1a, 2a and 3a show the respective kinematic designs.
The kinematic designs for the control of the punch/presser in machines; of this type present the following limitation:                if the machine is used with auxiliary tools positioned between the punch/presser and counter-punch or counter-blade (and in any other similar situation), the kinematic system works in unfavourable conditions, in which the pressing forces delivered are considerably reduced and insufficient (around_of the maximum force necessary) to guarantee the stability of all the sheet metal that can be processed on the machine (see figure of the kinematic system);        in the form of a graph provided to the users, the maximum limits (length, thickness, type of material) are defined for the use of auxiliary tools positioned between the punch/presser and counter-punch or counter-blade (see graph).        this kinematic system is currently a limitation to the development (greater lengths and thicknesses) of the range of electric panelling machines, due to the technical impossibility of emitting greater torque; overcoming this limitation would allow the gradual replacement of the hydraulic Express Bender (EB) machine with the more modern and performing EBe in all the sizes produced.        